Curing organopolysiloxanes with sulphur dichloride



- as polydimethylsiloxane, etc.

. United States Patent CURING ORGANOPOLYSILOXANES WITH SULPHUR DICHLORIDE Frank M. Precopio, Erie, Pa., assignor to General Electric 'Company, a corporation of New York No Drawing. Application April 13, 1956 Serial No. 577,925

8 Claims. (Cl. 117-232) "Thisinvention relates to cured, organopolysiloxanes and to the process of producing same. More particularly, this invention relates .to a rapid process for ouring organopolysiloxanes which comprises treating an organopolysiloxane with a sulfur dihalide such as sulfur dichloride (SCI and to the. products so formed.

Heretofore, organopolysiloxanes have been cured by many methods, for example by the curing action of various free radical agents, such as peroxides, etc. Although these processes are satisfactory, it is highly desirable tocure organopolysiloxanes with an inexpensive chemical agent that will cure organopolysiloxanes very rapidly without the application of heat.

,I have now discovered that organopolysiloxanes can be cured by a rapid, low temperature method which comprises treating an organopolysiloxane with a sulfur dihalidle such as SCl The versatility of this curing agent is demonstrated by the fact that it can cure both saturated and unsaturated organopolysiloxanes. Since organopo-lysiloxanes can be cured very rapidly (in less than a minute at room temperature) this invention is very attractive to commercial production. This short cure method is particularly useful in curing organopolysiloxanes of such cross-section that they can be exposed to vapors of Sci; and cured almost instantly.

In general, the process is carried out by exposing the orga'nopolysiloxane to either liquid SCl or its vapors. For example, when wire coated with an organopolysiloxane is passed through a tower containing an SO1 atmosphere, the coating contained thereon is cured within less than a minute. Thereupon,'any residual SCl is easily removed by exposing thecured organopolysiloxane to a stream of air or an inert gas. In this way an organopolysiloxane insulated wire is produced rapidly without heat.

Unexpectedly, I have discovered that SCl' is effective in curing both saturated and unsaturated organo-polysiloxanes. Thus, it is effective .in'curing such unsat urated organopolysiloxanes as vinyl, allyl, methallyl, etc. organopolysiloxanes as well as alkyl polysiloxanes such The curing action appears due to the unexpected versatile chemical reactivity of SCl In the case of the' unsaturated organopolysiloxanes, it'is possiblethat sulfur dichloride adds at the point of unsaturation so as to cross-link the organo-polysiloxane. Yet, even if there are no unsaturated groups present, it appears that sulfur dichloride replaces a hydrogen atom contained on the hydrocarbon moiety of theorganopolysiloxane. It appears that the reaction with the unsaturated group is more rapid than the saturated group. However, curing in both cases is very fast, fifteen secondsor less with-the unsaturated organopolysiloxane and thirty seconds or less with the saturated organopolysiloxane. In thevcase where the organopolysiloxane contains SiH or SiOH groups, reaction will also take place at this point. However, longer times can be used if desired, particularly Where a material of thicker cross section is employed.

- .Since SCI; is capable of reacting by both addition and substitution, any organopolysiloxane capable of reacting by either of these mechanisms can be used. Thus, organopolysiloxane oils, organopolysiloxane rubbers, and organopolysiloxane resins can be employed. Examples of these organopolysiloxanes can be found in,-'Rochow, Chemistry of Silicones, chap. 6, pp. 78-107, 2nd ed. (1951). j

Thus, organopolysiloxanes having the average structural formula: r

where the sum of a+b 1 to 3 and b hasa value of from 0 to l may beemployed. In this formula R represents saturated "-or unsaturated radicals selected from the group consisting of alkyl radical (e. g., methyl, ethyl, propyl,;butyl, isobutyl, amyl, hexyl, etc.), aryl radical .(e. g., phenyl, diphenyl, naphthyl, anthracyl, tolyl, xylyl, ethylphenyl, etc.), haloaryl-(e. g., chlorophenybfluorophenyl,etc.), aralkyl radical (e. g., benzyl, phenylethyl, etc.), a cycloalkyl radical (e. g., cyclopentyl, cyclohexyl', 1 etc. an unsaturated cycloaliphatic hydrocarbon radical (e. g., cyclopentenyl, cyclohexenyl, cyclopentadienyl, etc.), unsaturated aliphatic hydrocarbon radical (e, g., vinyl, allyl, methallyl, ethinyl, butadienyl, etc.), and mixtures thereof. The presence of halogens, for example, chlorine, fluorine, etc., on the organic radicals, particularly on the aryl radicals, is not precluded, Preferably R is methyl, vinyl or phenyl radical. Obviously, it will be apparent to those skilled in the art that.different types of organic radicals may be attached, to the same silicon atom or may be present in the organopolysiloxane molecule, as, for instance, both methyl and phenyl radicals, 'both methyl and ethyl radicals, -both ethyl-and phenyl radicals, etc. f 1

Examples of organohydrogen' polysiloxanes may be found, for instance, in Sauer Patents'2,595,890 .and 2,595,891; in .Wilcock Patent 2,491,843 and in Barry Patent'2,590,812..

Examples of organopolysiloxa'ne oils can 'be found for example, in Patnode Patent 2,469,888 and in'the Rochow text cited above. Examples of o-rganopolysiloxane gums can be found for example, in Agens 2,448,756; Sprung Patents 2,448,556, 2,484,595; Krieble 2,457,688; Hyde 2,490,357; Marsden 2,521,528 and Warrick 2,541,137, etc. Examples of resins can be found for instance in Rochow Patents 2,258,218 ,'2,258,222; Welsh 2,449,572; Bass 2,428,608, 2,446,177, etc. Even though these resins are already cross-linked, they maybe further reacted with SCl since they contain replaceable hydrogenatoms. For example, the resins can be dissolved in a solvent, applied to a surface of the solvent evaporated therefrom, and thereupon treated with SCI I Examples of unsaturated organopolysiloxanes fo'r ex ample are those disclosed in Roedel 2,420,911, Mars- I den*2,445,794, Hurd 2,645,628,'etc.' I

In. order that those skilled in the art may better understand how the'present invention may be practiced.

the'following 'examples are given by way of illustration and not byway of limitation. All parts are EXAMPLE '1 This example describes the preparation of low molecular weightorganopolysiloxanes containing silicon bonded vinyl radicals. A mixture of 1000 grams (6.2 moles) ,of redistilled methylvinyldiethoxysilane (boiling point 133 C. at:1.0 atmosphere, refractive index, n 1.40O1, density d 0.8620) and 1000 ml. of v6 Normal hydrochloric acidis refluxed for 72 hours. The resulting lower organopoly-;

siloxane phase is washed four times with distilled water,

tered. This results is a mixed methylvinylsiloxane oil containing both cyclic and linear methylvinylpolysiloxanes of varying chain lengths. This oil is distilled rapidly after 4 EXAMPLE 3 A vinyl-containing organopolysiloxane gum is prepared by adding 3 parts, by weight, of 1,3,5,7,9-pentamethyl- 1,3,5,7,9-pentavinylcyclopentasiloxane to 97 parts, by

resin to remove excess SCl d of 1 i p by W i i' if b 5 weight, of octamethylcyclotetrasiloxane and heating the a a pvolymenzanor} b ff z The dlstl l mixture to 135 C. At this point 0.05 percent, by weight, gigg ggiii 2 usugg g g g g T of cesium hydroxide is added and the mixture polymeriaed 1 me etween 1 at is to a gum within about 15 minutes. This vinyl-contaimng collected and after the addition of another one percent, um has the average Structural formula by weight, of p-tert-butyl catechol the distillate is fracg H tionated under reduced pressure ina by 16" pro- 2= )o.02s( a)1.974 $332231??? i fi i l i g g l g a In a similar fashion, gums containing 2.0 to 4.0 percent, mg a 0 g at m" by weight, of 1,3,5,7,9-pentamethyl-1,3',5,7,9-pentav1nyltlon boiling at 115 to 143 C. at 11,mm., and (3) a clopentasiloxane in octamethylcyclotetrasiloxane are ist.s stains: 13 -5. 572.23.122.21 1 3 5. e e gg g g merlzaloncaays wlc vary romaou lit:at?starter?easiest5f tiara? geg l ei e g g g o lsresuslnvny- 32.5 percent 51; to have a molecular weight of 346 by the average structural formulas v cryoscoplc determination using a solution of 0.240 gram 20 of the siloxane in 19.17 grams of cyclohexane, and a molar (CH2=CH)9-017(CH3)1883510 refractivity, MR 90.93. Theoretical values are 41.8 and I percent carbon, 7.02 percent hydrogen, 32.6 percent sili- I con, molecular weight 344.7, MR 91.20. Distillation (GHQ-CH)-35(CH3)1-965So of this compound in a small Vigreux column at atmosrespectively. pheric pressure without polymerization or decomposition EXAMPLE 4 shows its boiling point to be 224 to 224.5 C. at 758 mm.

Fraction 2 is washed with 25 ml. portions of 1 percent A gum contammg dlphenyl sfloxane umts PrBPaTetd sodium carbonate until the p-tert-butyl catechol is reby the methPd of Example for example by addlllg moved (as evidenced by a negative ferric chloride test Parts by f of 7 i on the aqueous solution). The oil is dried over anhycyclotetraslloxilnefl 47 Parts by e of 'octamethyl' drous potassium carbonate and distilled under reduced cyclotetraslloxane and'sopamt by welghb of o f pressure in a X protrudedtpacked column. cyclotetraslloxane to a temperature of about 150 C. and fiuafion yields 1 5 7 9 1 3 5 7 g i adding about 0.05 percent, by weight, of cesium hydroxide cyclopentasiloxane at 145 to 146 C. at 13 mm. This based on the total weght of the compound is analyzed and found to contain 41.6 percent Present In a matter of 10 to 20 mmutes a SHE is C, 7.2 percent H, and 32.8 percent Si, with a molecular formedweight of 437 and MR 113.58. Thiscompares to the EXAMPLE 5 theoretical values of 41.8 percent C, 7.02 percent H, 32.6 t I i percgrat Si, withla molecular lweighthof 430.18 and M R 40 g g j g fig ggggp ig,ggg itgxiingityilo p eniii ifiiii to sloxane an e ng e I V2 s gg g gfg gig giggj g g gg this time 0.05 percent, by weight, of cesium hydroxide 13 s 7 9 ll-hexamethyl 13 s 7 9 ll-hexavinylcyclohexaare m after 15. mmutes' a weght gum 18 obtained. Thls gum has the average structural siloxane whlch bolls between 160.5 and 161 C. at 5 mm. formula (CH (CH Sio Analysis of this compound shows it to contain 41.3 perg 2 3 L913 cent C, 7.1 percent H, 31.3 percent Si, with a molecular EXAMPLE 6 weight of 536 and MR 135.58. This compares with the t theoretical values of 41.8 percent C, 7.02 percent H, and 0 A vlnyl'eontalfllng 8 18 P p e y mlXlng grams 32.6 percent Si, with amolecular weight of 517.0 and MR of 1,3,5J-tetramethy1-1,3,5,7-tetravmylcyclotetraslloxane 136.80. This compound is distilled at atmospheric pressure P p y the methoq of Example 1 Wltb 97 grams and found to have a boiling point of 296 to 297 c. at of 0ctamethylcyclotetraslloxane about a o 750 mm. The boiling points, melting points, indices of tetrabutylphosphomum bydroxlde- T1115 mlXtuTe refraction and densities of the three compounds isolated heated to a temperature 0f about and after about above are listed in Table I. 15 minutes a high molecular weight gum is obtained.

Table I Fraction siloxane B. P., O. mm. M. P., 0. mi" 11;"

1 [(CH:)(CHz=CH)SiO]4 232% -43.5+0.1 1. 4342 0.9875 2 [(CHa)(CHa=CH)SiO] }-140 to 136 1.437s 0.9943 3 [(CH3)( H2=cH)sio]B ii }123 to -119 1.4400 1.0050

EXAMPLE-2 EXAMPLE 7 The-unfractionated oil, fraction 1, fraction 2 and frac- The gums prepared in Examples 3 through 6' are dis: tion 3 of the products of Example 1 are treated with solved in a suitable solvent (benzene, 50% solids) and vaporous SCI In each case a thin layer of the oil is applied to a suitable material (a piece of glass). The painted on a fiat surface (a piece of glass) which is exsolvent is thereafter allowed to evaporate. The resultposed to the vapors. A resinous product is immediately in'g film is thereupon exposed to vapors of SC1 to im formed. Thereupon a stream of air is passed over the mediately form a resinous product. Excess S01 is removed by a stream of air.

\ EXAMPLE 8 A cyclohexenyl polysiloxane is prepared byhydrolysing cyclohexenyl trichlorosilane. The resinous product is dissolved in toluene andSCl is bubbled into solution to immediately precipitate a light yellow, brittle resin.-- a

I EXAMPLE 9 A toluene solution of cyclohexenyl polysiloxane (prepared in Example 8) is applied to a piece of glass and a thin film is produced by evaporating the solvent therefrom. This film is exposed to SCl 'toproduce a hard, brittle resin. 1 a

EXAMPLE 10 Non-SO1 treated Xylene solutions containing 50% solids are'prepared'from the'organopolysiloxanes prepared in Examples 3, 4, 5, 6, and 8. A separate copper wire is passed through each solution, the solvent is evaporated therefrom by heat, the coated wire is then passed through a SC1 chamber, and residual SCl removed by a stream of air to produce an insulated wire.

In addition to the unsaturated organopolysiloxanes disclosed in the above examples, other unsaturated organopolysiloxanes can be used. Examples of suitable unsaturated vinyl-containing organopolysiloxanes are disclosed in Roedel2,420,91l, Marsden2,445,794, Hurd2,- 645,628, etc. It, of course, should beunderstood that in addition to the vinyl containing and cyclohexenyl containing organopolysiloxane disclosed above, allyllic, methallyllic, acetlylenic, polyunsaturates, etc. groups can also be employed. By controlling the amount of unsaturated groups present, one can produce a product having the desired toughness and flexibility.

a In addition to oils and gums, organopolysiloxane resins containing more than 1.0 and less than 2, preferably from about 1.11.7 hydrocarbon radicals attached directly to silicon can be reacted with sulfur dichloride. These compositions can be curedafter being applied to a surface as a solution and the solvent evaporated therefrom, or can be dissolved invthe solvent and precipitated by contacting the solution with sulfur dichloride.

The polysiloxane resins of this type are described, for example, in U. S. Patents 2,258,218-222 of Eugene G. Rochow. The resins, which comprise a plurality of hydrocarbon-substituted silicon atoms linked by oxygen atoms are prepared, for example, by hydrolysis and condensation of a mixture of organosilicon halides. Such resins usually contain small amounts of silicon-bonded hydroxyl or alkoxy groups as a result of the method of hydrolyzing the intermediate silanes used to prepare the polysiloxane. The commercially useful products containing an average of more than one and less than two hydrocarbon radicals per silicon atom are soluble in many solvents and are converted to a hard, insoluble state when heated for comparatively long periods of time at elevated temperatures. Other. examples of organopolysiloxane resins embraced within the scope of the present invention may be found described in Welsh Patent 2,449,572.-

EXAMPLE 11 An organopolysiloxane resin is prepared by cohydrolyzing 45.7 parts methyltrichlorosilane, 38.7 parts of phenyl trichlorosilane and 15.6 parts dimethyldichlorosilane, in the manner described in Welsh and Holdstock Patent 2,661,348. The resin thus obtained in the form 6 ,7 methyltrichlorosilane and 17.8 mole percent of silicon tetrachloride ishydrolyzed by adding a solution of 400 grams of these mixed silanes in 400 grams of methylisobutyl ketone to 1150 grams of water and cooled in an ice bath. The water is drawn off and 'the ketone solution diluted to a resin base content of 25% by the addition of the required amount of toluene. I

' This solution is painted on a piece of glass and the'solvent evaporated therefrom. This film is treated with $01 to yieldahard resin. 7

EXAMPLE 13 A silicone resin is prepared by cohydrolyzing a blend ofSO mole percent of methyltrichloros'ilane, 30: mole percent 'of phenylt richlorosilane"and 20 mole percentof dimethyldichlorosilane with water in thepresence of butyl alcohol. The resulting product is heat treated with a small amount of zinc octoate. A solution of this product in xylene is prepared and painted on a piece of glass and the solvent evaporated therefrom. This film is treated with SCl to yield a hard resin.

The resinous products of this invention can be used in any of the various applications in which organopolysiloxane resins have previously been used. For example, they may be used as electrical insulation, wire enamels, in the manufacture of paints, as impregnating and coating compositions for sheet material, etc.

What I claim as as new and desire to secure by Letters Patent of the United States is:

1. A process of curing an organopolysiloxane having the formula members selected from the class consisting of alkyl radicals, aryl radicals, haloaryl radicals, aralkyl radicals,

. cycloalkyl radicals, unsaturated cycloalipha'tic hydroof 60 percent solids in xylene solution upon treatment with SCl immediately precipitates from solution.

This'solution is also painted on a piece of glass and the solvent evaporated therefrom. This film, upon treatment with SCl forms a hard resin.

EXAMPLE 12 A mixture of chlorosilanes consisting of 59.4 mole percent of dimethyldichlorosilane, 22.8 mole percent of carbon radicals, and unsaturated aliphatic hydrocarbon radicals, which process comprises contacting the said organopolysiloxane with sulfur dichloride.

2. A process of curing an organopolysiloxane having the formula 4. The method of curing an organopolysiloxane gum in which the organic groups are methyl radicals, phenyl radicals, and vinyl radicals, which method comprises contacting said organopolysiloxane with sulfur dichloride.

5. The method of curing a methylpolysiloxane resin which comprises contacting said resin with sulfur di-' chloride.

6. The method of curing a methylphenylpolysiloxane resin which comprises contacting said resin with sulfur dichloride. I

7. The method of coating a surface which comprises forming a film on said surface of an uncured organopolysiloxane having the formula where the sum of a+b is'equal to from 1 to 3, inclusive,

7 b has a value of from 0 to 1, inclusive, and R represents members selected from the class consisting of alkyl radicals, aryl radicals, ,haloaryl radicals, aralkyl-radicals, cycloalkyl radicals, unsaturated cycloaliphatic hydrocarbonvradi cals, and unsaturated aliphatic hydrocarbon radicals, and subsequently. exposing the resulting coated surface to the vapors of sulfur dichloride.- I V ,8. The method of making an insulated electrical conductor which comprises forming a solution of an organepolysiloxane having the formula members selected from the class consisting of alkyl radi cals, aryl radicals, haloaryl radicals, aralkyl radicals, cycloalkyl radicals, unsaturated cycloaliphatic hydrocarbon radicals, and unsaturated aliphatic hydrocarbon radicals, applying said solution to a copper Wire, evaporating the solvent from said solution, whereby a coating of the uncured organopolysiloxane is formed on said vvir'e', contacting the surface of said coated Wire with sulfur *di chloride, and removing any residual sulfur dichloride from the resulting coated conductor. 4

References Cited in the file of this'pa'tent Hurd July 14, 1953 

8. THE METHOD OF MAKING AN INSULATED ELECTRICAL CONDUCTOR WHICH COMPRISES FORMING A SOLUTION OF AN ORGANOPOLYSILOXANE HAVING THE FORMULA 